netinet*: replace IP6_EXTHDR_GET()

In a few places we have IP6_EXTHDR_GET() left in upper layer protocols.
The IP6_EXTHDR_GET() macro might perform an m_pulldown() in case the data
fragment is not contiguous.

Convert these last remaining instances into m_pullup()s instead.
In CARP, for example, we will a few lines later call m_pullup() anyway,
the IPsec code coming from OpenBSD would otherwise have done the m_pullup()
and are copying the data a bit later anyway, so pulling it in seems no
better or worse.

Note: this leaves very few m_pulldown() cases behind in the tree and we
might want to consider removing them as well to make mbuf management
easier again on a path to variable size mbufs, especially given
m_pulldown() still has an issue not re-checking M_WRITEABLE().

Reviewed by:	gallatin
MFC after:	8 weeks
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D22335

sys/netinet/ip_carp.c

@@ -567,12 +567,13 @@ carp6_input(struct mbuf **mp, int *offp, int proto)
 
 	/* verify that we have a complete carp packet */
 	len = m->m_len;
-	IP6_EXTHDR_GET(ch, struct carp_header *, m, *offp, sizeof(*ch));
+	m = m_pullup(m, *offp + sizeof(*ch));
-	if (ch == NULL) {
+	if (m == NULL) {
 		CARPSTATS_INC(carps_badlen);
 		CARP_DEBUG("%s: packet size %u too small\n", __func__, len);
 		return (IPPROTO_DONE);
 	}
+	ch = (struct carp_header *)(mtod(m, caddr_t) + *offp);
 
 
 	/* verify the CARP checksum */

sys/netinet6/sctp6_usrreq.c

@@ -103,13 +103,13 @@ sctp6_input_with_port(struct mbuf **i_pak, int *offp, uint16_t port)
 	SCTP_STAT_INCR_COUNTER64(sctps_inpackets);
 	/* Get IP, SCTP, and first chunk header together in the first mbuf. */
 	offset = iphlen + sizeof(struct sctphdr) + sizeof(struct sctp_chunkhdr);
-	ip6 = mtod(m, struct ip6_hdr *);
+	m = m_pullup(m, offset);
-	IP6_EXTHDR_GET(sh, struct sctphdr *, m, iphlen,
+	if (m == NULL) {
-	    (int)(sizeof(struct sctphdr) + sizeof(struct sctp_chunkhdr)));
-	if (sh == NULL) {
 		SCTP_STAT_INCR(sctps_hdrops);
 		return (IPPROTO_DONE);
 	}
+	ip6 = mtod(m, struct ip6_hdr *);
+	sh = (struct sctphdr *)(mtod(m, caddr_t) + iphlen);
 	ch = (struct sctp_chunkhdr *)((caddr_t)sh + sizeof(struct sctphdr));
 	offset -= sizeof(struct sctp_chunkhdr);
 	memset(&src, 0, sizeof(struct sockaddr_in6));

sys/netipsec/xform_ah.c

@@ -575,14 +575,14 @@ ah_input(struct mbuf *m, struct secasvar *sav, int skip, int protoff)
 	/* Figure out header size. */
 	rplen = HDRSIZE(sav);
 
-	/* XXX don't pullup, just copy header */
+	m = m_pullup(m, skip + rplen);
-	IP6_EXTHDR_GET(ah, struct newah *, m, skip, rplen);
+	if (m == NULL) {
-	if (ah == NULL) {
 		DPRINTF(("ah_input: cannot pullup header\n"));
 		AHSTAT_INC(ahs_hdrops);		/*XXX*/
 		error = ENOBUFS;
 		goto bad;
 	}
+	ah = (struct newah *)(mtod(m, caddr_t) + skip);
 
 	/* Check replay window, if applicable. */
 	SECASVAR_LOCK(sav);

sys/netipsec/xform_esp.c

@@ -307,8 +307,15 @@ esp_input(struct mbuf *m, struct secasvar *sav, int skip, int protoff)
 		ESPSTAT_INC(esps_badilen);
 		goto bad;
 	}
-	/* XXX don't pullup, just copy header */
+
-	IP6_EXTHDR_GET(esp, struct newesp *, m, skip, sizeof (struct newesp));
+	m = m_pullup(m, skip + sizeof(*esp));
+	if (m == NULL) {
+		DPRINTF(("%s: cannot pullup header\n", __func__));
+		ESPSTAT_INC(esps_hdrops);	/*XXX*/
+		error = ENOBUFS;
+		goto bad;
+	}
+	esp = (struct newesp *)(mtod(m, caddr_t) + skip);
 
 	esph = sav->tdb_authalgxform;
 	espx = sav->tdb_encalgxform;